Want to do the environmentally responsible thing and install a drought tolerant landscape? The first thing you could do is rip out your lawn and install trees, shrubs and ground cover. Generally, this act alone will save you about a third of your monthly water use. The caveat being is that you must not water your newly planted trees, shrubs, and groundcover the same amount as your newly removed lawn or you will not save any water at all.

However, you must give your new landscape some water to keep it alive and healthy. How much? Therein lies the rub. I don’t know. I have over 25 years experience as a landscape architect and I’m regarded as one of the many experts in exterior water conservation in California, yet I cannot guarantee the water usage of any landscape I design for you.

Why? Because no one really knows.

How can this be? Because the mixed-bed landscape ecosystems – trees, shrubs, and ground cover – from around the world are very complex, and there’s never been any funded field research to determine averages and amounts. The closest thing we have is a study called WUCOLS.

In the early ’90s, the University of California Cooperative Extension and the California Department of Water Resources teamed to create what eventually became the definitive reference for plant water usage in California: the Water Use Classification of Landscape Species study – or WUCOLS for short.

WUCOLS is comprised of two parts: it’s a formula for calculating plant water use in California with a fairly comprehensive list, rating plants from “very low” to “high” water requirements. In the last 25 years since it was published, WUCOLS has been updated 4 times. The list has become an integral part of the State’s landscape water conservation efforts, as well as an integral part of major sustainable scoring systems like LEED, SITES, and the Living Building Challenge. The study’s authors never imagined their creation would be used to define plant water conservation not only in California, but around the world.

WUCOLS was originally meant to be just a guide. As such, the study is beginning to show signs of not being able to hold up to the scrutiny necessary to be the basis for water conservation laws in the State and around the Country.

This is not to say that the original study was not valid or rigorous. With a limited budget, the authors worked with what they had. They convened with experts from five different bio-regions around the state to evaluate nursery-available plants. They also used existing field studies wherever possible to help guide their evaluations.

Still, most of the plants on the WUCOLS list are rated based on anecdotal evidence rather than true field research data. This has become a problem as most of the water districts and municipalities write into their ordinances requirements that only plants rated by WUCOLS as “very low” and “low” can be planted within their jurisdiction.

In an attempt to finally add a more rigorous data to WUCOLS, the UC Cooperative Extension and the Department of Water Resources has been conducting a survey of 1,500 ornamental landscape sites around the state. They will announce their findings at a meeting on December 6th at the Metropolitan Water District Headquarters, adjacent to LA Union Station.

If we are serious about wanting to use our water resources responsibly while still maintaining the beauty of our state, we must be able to give landowners and designers the tools to be able to make the best decisions benefitting landscapes. The only way to accomplish this lofty goal is to provide the people of California with vetted research that generates hard and reliable data.

WUCOLS will now be moving forward to becoming that tool. AHBE Landscape Architects is proud to be the sponsor for this event. Please look for more information about this event in this space, and through announcements with our partner organizations: USGBC, Living Building Challenge, and ASLA.

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AHBE LAB is a forum for exploration, inquiry, and collaboration. It is a place to share who we are, what inspires us, what we are dreaming about. We hope you enjoy this glimpse into our design process.